Stack Array implementation of Java

Question

This is my array implementation on stack in Java. It involves push, pop, get and growth when limit of array size is reached.

I am a self-taught programmer starting to learn data structures and algorithms.

I am looking for

1. any recommendation on conventions
2. an honest opinion on how bad this piece of code if this is an interview.
3. anything wrong and room for improvement.

I wrote this code myself, not looking at any other similar questions on Code Review.

public class stackAlist{ int[] data; int size; static int growthmultipler = 1; public stackAlist(){ data = new int[2*growthmultipler]; size = 0; } public void push(int value){ if(this.size == 0){ this.data[0] = value; this.size += 1; this.growthmultipler = 1; } else if(this.size == 2*growthmultipler){ growthmultipler += 1; stackAlist newlist = new stackAlist(); newlist.data = new int[2*growthmultipler]; System.arraycopy(this.data, 0, newlist.data, 0, this.size); this.data = newlist.data; this.data[size] = value; this.size += 1; } else{ this.data[size] = value; this.size += 1; } } public void pop(){ this.data[size-1] = 0; this.size = this.size-1; } public void get(){ int i; for(i =0; i < this.size; i++){ System.out.println(data[i]); } } public static void main(String[] args){ stackAlist a = new stackAlist(); a.push(1); a.push(2); a.get(); a.pop(); a.get(); a.push(3); a.push(4); a.get(); } } 

Answer 1

First of all, you are using a static variable (growthmultipler) inside the instance of a class. This is fatal if you have more than one instance of this class. Because you always use 2*growthmultipler, you don't need it. Use +=2 instead.

You don't need to prealloc data in the constructor. It will be done if it's needed.

You don't need to handle "size == 0" separately. You only have to handle "size >= length".

You don't have to create a new class if you want to grow data.

In pop() you should test to not get negative (and throw an exception). And normally a pop function returns the value.

In summary it might look like this:

public class stackAlist{ int[] data; int size; public stackAlist(){ size = 0; data = new int[size]; } public void push(int value){ if(size>=data.length) { int [] ndata = new int[data.length+2]; System.arraycopy(data, 0, ndata, 0, size); data = ndata; } data[size] = value; size += 1; } public int pop() { int ret=0; if(size>0) { size -= 1; ret = data[size]; data[size] = 0; } return ret; } ..... 

Answer 2

A couple things to add:

1. Classes should use CamelCase and should preferably have descriptive names. stackAlist would be better named ArrayStack.
2. You might want to have a Stack interface that ArrayStack implements.
3. You might want to extract the resizing code into a separate method, and optionally make it public and/or take parameters.
4. In your pop method, there's no need to zero out the popped items.